The reentrant wideband bandpass/bandstop elliptic filters

This paper presents a novel wideband bandpass/bandstop filter configuration. The new filter is based on the reentrant structure with unequal dielectric constants of the internal and external filling. As a result, additional symmetrical transmission zeros are generated at the lower and upper stop bands of the bandpass filter leading to elliptic function response that improves the pass band and selectivity. The same conclusions are formulated about the bandstop filter in terms of return loss. The general TEM circuit models for the proposed filters in terms of a series connection of the two-ports are presented and then used to determine its electrical parameters. An experimental prototype has been fabricated using conventional printed circuit board technology. Measured S-parameters show acceptable agreement with analytical and full-wave simulations, showing promising potential for a variety of applications.